1. Field of the Invention
The invention relates to a vehicle airbag device in which an airbag is provided with a vent hole.
2. Description of the Related Art
Japanese Patent Application Publication No. 2002-2439 (JP-A-2002-2439) discloses a structure that mechanically controls the opening and closing of vent holes formed in an airbag corresponding to whether or not an occupant is wearing webbing. This related technology will be briefly described. That is, in an airbag device for a passenger seat, vent holes are formed at three locations in the airbag, concretely, the left and right side surfaces and an upper surface of the airbag. Incidentally, the upper surface of the airbag substantially faces the windshield pane.
According to the foregoing construction, in the case where an occupant is wearing webbing at the time of a frontal collision, the occupant is restrained by the webbing, so that the occupant's head moves forward and obliquely downward relative to the vehicle, by inertia. Then, the occupant's upper body that includes the head is received by the airbag. In this case, the upper surface of the airbag does not contact the windshield pane, so that the gas is let out from the three vent holes, and thus the bag internal pressure is appropriately lowered. On the other hand, in the case where an occupant is not wearing the webbing, since the occupant is not restricted by the webbing, the occupant's head moves to a vehicle front side by inertia at the time of a frontal collision. Therefore, the airbag is immediately pressed to the vehicle front side, so that the upper surface of the airbag strongly contacts the windshield pane. Thus, the vent hole provided in the upper surface is closed, so that the bag internal pressure heightens.
However, according to the construction disclosed in the foregoing related technology, the vent hole additionally provided in a central portion of the upper surface of the airbag is closed by the windshield pane, and therefore there is a problem as follows. For example, when a vehicle undergoes a frontal collision at a obliquely front side (undergoes an oblique collision), the occupant's head moves to an obliquely front side of the vehicle by inertia. Hence, the occupant's head is received by an end portion of the airbag in the width direction of the vehicle. In this case, it is conceivable that the airbag is pushed in a vehicle width direction in a plan view so that the vent hole may open.
Besides, since the foregoing airbag is constructed so that the vent hole formed at the center of the upper surface of the airbag is closed from outside the airbag by utilizing the windshield pane, there is a possibility that a gap may form between the vent hole and the windshield pane so that the vent hole cannot be closed, depending on the curved surface shape of the windshield pane, or the curved surface shape of the upper surface of the airbag at the time of inflation and deployment.